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Yesterday Lydia and I stumbled over #1906. In a first
approach I thought that this was caused by a bug in
Sequenced.seqno_changed() (happening when I have two items
having seqno 1 and 2. Then I call MoveDown on the first. Or I manually
set its seqno to 2.) I created a new test case test_sequenced
in apc demo project. Which shows that this was a wrong track. There
is no bug.
Another possible explanation is simply that
lino_xl.lib.vat.VatRules was not ordered.